The Kuiper belt is a collection of small bodies (Kuiper belt objects, KBOs) that lie beyond the orbit of Neptune and which are believed to have formed contemporaneously with the planets. Their small size and great distance make them difficult to study. KBO 55636 (2002 TX300) is a member of the water-ice-rich Haumea KBO collisional family(1). The Haumea family are among the most highly reflective objects in the Solar System. Dynamical calculations indicate that the collision that created KBO 55636 occurred at least 1 Gyr ago(2,3). Here we report observations of a multi-chord stellar occultation by KBO 55636, which occurred on 9 October 2009 UT. We find that it has a mean radius of 143 +/- 65 km (assuming a circular solution). Allowing for possible elliptical shapes, we find a geometric albedo of 0.88(0.06)(+0.15) in the V photometric band, which establishes that KBO 55636 is smaller than previously thought and that, like its parent body, it is highly reflective. The dynamical age implies either that KBO 55636 has an active resurfacing mechanism, or that fresh water-ice in the outer Solar System can persist for gigayear timescales.

We present an ultra-deep survey for Neptune Trojans using the Subaru 8.2 m and Magellan 6.5 m telescopes. The survey reached a 50% detection efficiency in the R band at m(R) = 25.7 mag and covered 49 deg(2) of sky. m(R) = 25.7 mag corresponds to Neptune Trojans that are about 16 km in radius (assuming an albedo of 0.05). A paucity of smaller Neptune Trojans (radii < 45 km) compared with larger ones was found. The brightest Neptune Trojans appear to follow a steep power-law slope (q = 5 +/- 1) similar to the brightest objects in the other known stable reservoirs such as the Kuiper Belt, Jupiter Trojans, and main belt asteroids. We find a roll-over for the Neptune Trojans that occurs around a radius of r = 45 +/- 10 km (m(R) = 23.5 +/- 0.3), which is also very similar to the other stable reservoirs. All the observed stable regions in the solar system show evidence for Missing Intermediate-Sized Planetesimals (MISPs). This indicates a primordial and not collisional origin, which suggests that planetesimal formation proceeded directly from small to large objects. The scarcity of intermediate-and smaller-sized Neptune Trojans may limit them as being a strong source for the short period comets.

We consider the application of interferometry to measuring the sizes and shapes of small bodies in the Solar System that cannot be spatially resolved by today's single-dish telescopes. Assuming ellipsoidal shapes, we provide a formalism to derive the shape parameters from visibility measurements along three different baseline orientations. Our results indicate that interferometers can measure the size of an object to better than 15% uncertainty if the limb-darkening is unknown. Assuming a Minnaert scattering model, one can theoretically derive the limb-darkening parameters from simultaneous measurements of visibilities at several different projected baseline lengths to improve the size and shape determination to an accuracy of a few percent. The best size measurement can be reached when one axis of the object's projected disk is aligned with one baseline orientation, and the measurement of cross-sectional area is independent of baseline orientation. We construct a 3-D shape model for the dwarf planet Haumea and use it to synthesize interferometric data sets. Using the Haumea model, we demonstrate that when photometric light curve, visibility light curve, and visibility phase center displacement are combined, the rotational period and sense of rotation can all be derived, and the rotational pole can be estimated. Because of its elongated shape and the dark red spot, the rotation of Haumea causes its optical photocenter to move in a loop on the sky. Our simulations show that this loop has an extend of about 80 mu as without the dark red spot, and about 200 mu as with it. Such movements are easily detectable by space-based astrometric interferometer designed e.g. for planet detection. As an example, we consider the possible contributions to the study of small bodies in the Solar System by the Space Interferometry Mission. We show that such a mission could make substantial contributions in characterizing the fundamental physical properties of the brightest Kuiper Belt Objects and Centaurs as well as a large number of main belt asteroids. We compile a list of Kuiper Belt Objects and Centaurs that are potentially scientifically interesting and observable by such missions. (C) 2010 Elsevier Inc. All rights reserved.

We present a new near-infrared photometric system for detection of water ice and methane ice in the solar system. The system consists of two medium-band filters in the K-band region of the near-infrared, which are sensitive to water ice and methane ice, plus continuum observations in the J band and Y band. The primary purpose of this system is to distinguish between three basic types of Kuiper Belt Objects (KBOs)-those rich in water ice, those rich in methane ice, and those with little absorbance. In this work, we present proof-of-concept observations of 51 KBOs using our filter system, 21 of which have never been observed in the near-infrared spectroscopically. We show that our custom photometric system is consistent with previous spectroscopic observations while reducing telescope observing time by a factor of similar to 3. We use our filters to identify Haumea collisional family members, which are thought to be collisional remnants of a much larger body and are characterized by large fractions of water ice on their surfaces. We add 2009 YE7 to the Haumea collisional family based on our water ice band observations (J - H2O = -1.03 +/- 0.27) which indicate a high amount of water ice absorption, our calculated proper orbital elements, and the neutral optical colors we measured, V - R = 0.38 +/- 0.04, which are all consistent with the rest of the Haumea family. We identify several objects dynamically similar to Haumea as being distinct from the Haumea family as they do not have water ice on their surfaces. In addition, we find that only the largest KBOs have methane ice, and Haumea itself has significantly less water ice absorption than the smaller Haumea family members. We find no evidence for other families in the Kuiper Belt.

In 2009, we used the Subaru telescope to observe all the faint irregular satellites of Neptune for the first time since 2004. These observations extend the data arcs for Halimede, Psamathe, Sao, Laomedeia, and Neso from a few years to nearly a decade. We also report on a search for unknown Neptune satellites in a half-square degree of sky and a limiting magnitude of 26.2 in the R band. No new satellites of Neptune were found. We numerically integrate the orbits for the five irregulars and summarize the results of the orbital fits in terms of the state vectors, post-fit residuals, and mean orbital elements. Sao and Neso are confirmed to be Kozai librators, while Psamathe is a "reverse circulator." Halimede and Laomedeia do not seem to experience any strong resonant effects.

About 2500 deg(2) of sky south of declination -25 degrees and/or near the Galactic Plane were surveyed for bright outer solar system objects. This survey is one of the first large-scale southern sky and Galactic Plane surveys to detect dwarf planets and other bright Kuiper Belt Objects in the trans-Neptunian region. The survey was able to obtain a limiting R-band magnitude of 21.6. In all, 18 outer solar system objects were detected, including Pluto which was detected near the Galactic center using optimal image subtraction techniques to remove the high stellar density background. Fourteen of the detections were previously unknown trans-Neptunian objects, demonstrating that the southern sky had not been well searched to date for bright outer solar system objects. Assuming moderate albedos, several of the new discoveries from this survey could be in hydrostatic equilibrium and thus could be considered dwarf planets. Combining this survey with previous surveys from the northern hemisphere suggests that the Kuiper Belt is nearly complete to around 21st magnitude in the R band. All the main dynamical classes in the Kuiper Belt are occupied by at least one dwarf-planet-sized object. The 3:2 Neptune resonance, which is the innermost well-populated Neptune resonance, has several large objects while the main outer Neptune resonances such as the 5:3, 7:4, 2:1, and 5:2 do not appear to have any large objects. This indicates that the outer resonances are either significantly depleted in objects relative to the 3:2 resonance or have a significantly different assortment of objects than the 3:2 resonance. For the largest objects (H < 4.5 mag), the scattered disk population appears to have a few times more objects than the main Kuiper Belt (MKB) population, while the Sedna population could be several times more than that of the MKB.

Kuiper Belt object 2007 TY430 is the first wide, equal-sized, binary known in the 3: 2 mean motion resonance with Neptune. The two components have a maximum separation of about 1 arcsec and are on average less than 0.1 mag different in apparent magnitude with identical ultra-red colors (g - i = 1.49 +/- 0.01 mag). Using nearly monthly observations of 2007 TY430 from 2007 to 2011, the orbit of the mutual components was found to have a period of 961.2 +/- 4.6 days with a semi-major axis of 21000 +/- 160 km and eccentricity of 0.1529 +/- 0.0028. The inclination with respect to the ecliptic is 15.68 +/- 0.22 deg and extensive observations have allowed the mirror orbit to be eliminated as a possibility. The total mass for the binary system was found to be 7.90 +/- 0.21 x 10(17) kg. Equal-sized, wide binaries and ultra-red colors are common in the low-inclination "cold" classical part of the Kuiper Belt and likely formed through some sort of three-body interactions within a much denser Kuiper Belt. To date 2007 TY430 is the only ultra-red, equal-sized binary known outside of the classical Kuiper Belt population. Numerical simulations suggest 2007 TY430 is moderately unstable in the outer part of the 3:2 resonance and thus 2007 TY430 is likely an escaped "cold" classical object that later got trapped in the 3:2 resonance. Similar to the known equal-sized, wide binaries in the cold classical population, the binary 2007 TY430 requires a high albedo and very low density structure to obtain the total mass found for the pair. For a realistic minimum density of 0.5 g cm(-3) the albedo of 2007 TY430 would be greater than 0.17. For reasonable densities, the radii of either component should be less than 60 km, and thus the relatively low eccentricity of the binary is interesting since no tides should be operating on the bodies at their large distances from each other. The low prograde inclination of the binary also makes it unlikely that the Kozai mechanism could have altered the orbit, making the 2007 TY430 binary orbit likely one of the few relatively unaltered primordial binary orbits known. Under some binary formation models, the low-inclination prograde orbit of the 2007 TY430 binary indicates formation within a relatively high velocity regime in the Kuiper Belt.

The optical colors of 58 objects in mean motion resonance with Neptune were obtained. The various Neptune resonant populations were found to have significantly different surface color distributions. The 5:3 and 7:4 resonances have semimajor axes near the middle of the main Kuiper Belt and both are dominated by ultra-red material (spectral gradient: S greater than or similar to 25). The 5:3 and 7:4 resonances have statistically the same color distribution as the low-inclination "cold" classical belt. The inner 4:3 and distant 5:2 resonances have objects with mostly moderately red colors (S similar to 15), similar to the scattered and detached disk populations. The 2:1 resonance, which is near the outer edge of the main Kuiper Belt, has a large range of colors with similar numbers of moderately red and ultra-red objects at all inclinations. The 2:1 resonance was also found to have a very rare neutral colored object showing that the 2:1 resonance is really a mix of all object types. The inner 3:2 resonance, like the outer 2:1, has a large range of objects from neutral to ultra-red. The Neptune Trojans (1:1 resonance) are only slightly red (S similar to 9), similar to the Jupiter Trojans. The inner 5:4 resonance only has four objects with measured colors but shows equal numbers of ultra-red and moderately red objects. The 9:5, 12:5, 7:3, 3:1, and 11:3 resonances do not have reliable color distribution statistics since few objects have been observed in these resonances, though it appears noteworthy that all three of the measured 3:1 objects have only moderately red colors, similar to the 4:3 and 5:2 resonances. The different color distributions of objects in mean motion resonance with Neptune are likely a result from the disruption of the primordial Kuiper Belt from the scattering and migration of the giant planets. The few low-inclination objects known in the outer 2:1 and 5:2 resonances are mostly only moderately red. This suggests if the 2:1 and 5:2 have a cold low-inclination component, the objects likely had a significantly different origin than the ultra-red-dominated cold components of the cold classical belt and 5:3 and 7:4 resonances.

We report the discovery of 87 new T dwarfs uncovered with the Wide-field Infrared Survey Explorer (WISE) and 3 brown dwarfs with extremely red near-infrared colors that exhibit characteristics of both L and T dwarfs. Two of the new T dwarfs are likely binaries with L7 +/- 1 primaries and mid-type T secondaries. In addition, our follow-up program has confirmed 10 previously identified T dwarfs and 4 photometrically selected L and T dwarf candidates in the literature. This sample, along with the previous WISE discoveries, triples the number of known brown dwarfs with spectral types later than T5. Using the WISE All-Sky Source Catalog we present updated color-color and color-type diagrams for all the WISE-discovered T and Y dwarfs. Near-infrared spectra of the new discoveries are presented along with spectral classifications. To accommodate later T dwarfs we have modified the integrated flux method of determining spectral indices to instead use the median flux. Furthermore, a newly defined J-narrow index differentiates the early-type Y dwarfs from late-type T dwarfs based on the J-band continuum slope. The K/J indices for this expanded sample show that 32% of late-type T dwarfs have suppressed K-band flux and are blue relative to the spectral standards, while only 11% are redder than the standards. Comparison of the Y/J and K/J index to models suggests diverse atmospheric conditions and supports the possible re-emergence of clouds after the L/T transition. We also discuss peculiar brown dwarfs and candidates that were found not to be substellar, including two young stellar objects and two active galactic nuclei. The substantial increase in the number of known late-type T dwarfs provides a population that will be used to test models of cold atmospheres and star formation. The coolest WISE-discovered brown dwarfs are the closest of their type and will remain the only sample of their kind for many years to come.